Project Summary MAP kinases (MAPKs) are regulatory components of many signal transduction pathways that impact eukaryotic cell growth, differentiation, and movement. Structurally related atypical MAPKs, represented by mammalian MAPK15 (also known as Erk8) and Dictyostelium Erk2, are not activated by conventional MAPK kinases but rather by some unknown mechanism and little is known about the cellular targets and responses regulated by atypical MAPKs. Our recent creation and analysis of a Dictyostelium erk2- null mutant indicates that Erk2 is essential for chemotactic movement to multiple signals. In collaboration with others, we have also determined that Erk2 can phosphorylate and translocate the GATA transcription factor, GtaC, from the nucleus to the cytoplasm. The proposed research will investigate the mechanisms of atypical MAPK regulation and function using genetic and biochemical approaches. Erk2 mutants will be analyzed for their ability to be activated in response to chemotactic stimulation. Erk2 regulation of GtaC will be investigated to define atypical MAPK docking and phosphorylation sites. A real-time fluorescent reporter based on the Erk2 regulation of GtaC nuclear/cytoplasmic shuttling will be used to investigate atypical MAPK activity in single cells during chemotaxis and cell differentiation. The results of this project are expected to identify specific mechanisms of atypical MAPK regulation and function and also provide insight into the role of atypical MAPK signaling in signaling pathways that regulate chemotactic responses and cellular differentiation. The project will also develop atypical MAPK reporter technology that could benefit the analysis of atypical MAPK function in other eukaryotes.